Role of membrane transport of water and glycerol in the freeze tolerance of the rice stem borer, Chilo suppressalis Walker (Lepidoptera: Pyralidae)

Abstract

Overwintering larvae of the rice stem borer, Chilo suppressalis accumulate glycerol and are freezing tolerant to about -25°C. However, non-diapausing larvae cannot accumulate glycerol and are killed by freezing. We compared the extent of tissue damage, the effects of glycerol concentration, and the transport of glycerol and water in fat body tissues from these larvae at selected freezing temperatures. Tissues from overwintering larvae, but not non-diapausing larvae, survive when frozen at -20°C with 0.25M glycerol, but the protection afforded by glycerol is offset by the water-channel inhibitor mercuric chloride. Glycerol in higher concentration (0.75M) affords some protection even to the fat body of non-diapausing larvae. Radiotracer assays of overwintering larvae show that water leaves the tissues during freezing while glycerol enters, and that mercuric chloride disrupts this process. Transport is also disrupted after lethal freezing at -35°C. Therefore, membrane transport of water and glycerol is involved in the avoidance of freezing injury to fat body cells of the rice stem borer, apparently by mediating the replacement of water with glycerol in freezing-tolerant tissues.

Aquaporins play a role in desiccation and freeze tolerance in larvae of the goldenrod gall fly, Eurosta solidaginis

“…RNA insertion and protein overexpression of aquaporins successfully increases the survival of mouse oocytes during cryopreservation (Edashige, 2003) and the viability of baker's yeast in bread dough after freezing (Tanghe et al, 2002). In addition, a recent report by Izumi et al (Izumi et al, 2006) provides evidence that aquaporins promote freeze tolerance in a rice stem boring insect. By blocking the functionality of the protein with mercuric chloride, a known inhibitor of some aquaporins (Preston et al, 1993), they reported a reduction in cell survival during freezing.…”

The protective role of aquaporins in the freeze-tolerant insect Eurosta solidaginis: functional characterization and tissue abundance of EsAQP1

“…The permeability of AQP/GLPs to these molecules implicates these proteins in protecting against freeze-induced damage in a range of organisms, including yeast (Tanghe et al, 2002), insects (Izumi et al, 2006;Philip et al, 2008) and amphibians (Zimmerman et al, 2007). The ability of EsAQP1 channels to redistribute water across the membrane faster than by simple diffusion through membrane, as shown by our in vitro assay (Fig.4), would facilitate cellular dehydration that is caused by the formation of concentrated extracellular fluid during freezing.…”

“…AQPs, which rapidly redistribute water and certain small solutes across the membrane, are associated with the physiological response to stresses that require the management of cellular water, such as anhydrobiosis (Kikawada et al, 2008), feeding on osmotically challenging foods (Le Caherec et al, 1996;Shakesby et al, 2009) and survival of freezing (Izumi et al, 2006;Philip et al, 2008;Philip and Lee, 2010). To better understand the role of these proteins in osmotic stress, we identified, functionally characterized the water permeability and determined the tissue distribution of an AQP during seasonal cold acclimation in E. solidaginis.…”

“…<35%) (Davis and Lee, 2001), one could argue this tissue does not require EsAQP1 in high abundance for rapid redistribution of water during freezing. Although this is a plausible explanation, the results from previous studies suggest that AQPs and/or GLPs are present in fat body, as this tissue loses its ability to tolerate freezing when frozen in the presence of an AQP inhibitor (Izumi et al, 2006;Philip et al, 2008). Furthermore, fat body is the site of glycerol biosynthesis (Kukal et al, 1988), which likely necessitates a high abundance of GLPs.…”

“…Aquaglyceroporins (GLPs), a subgroup of AQPs permeable to water and small uncharged solutes (Borgnia et al, 1999), are implicated in the cellular movement of glycerol during freezing (Izumi et al, 2006;Philip and Lee, 2010;Philip et al, 2008;Zimmerman et al, 2007). The importance of glycerol uptake through GLPs in freezing survival is suggested by the improved cryopreservation survival of mouse oocytes that artificially express GLPs (Edashige et al, 2003).…”